Tip gap and coolant mass flux ratio effects on film cooling effectiveness, coefficients of convection, and net heat flux reduction along a transonic turbine airfoil

Abstract

Considered are coefficient of convection, adiabatic effectiveness, and net heat flux reduction characteristics for the extremity end of a transonic turbine airfoil with a squealer rim and coolant films. A cascade that is linear is employed to mount the airfoil along with four additional airfoils. Subsonic conditions are present along the concave side of each considered turbine airfoil, and transonic conditions are present along the convex side of each considered turbine airfoil. Included are spatially-resolved and line-averaged variations of surface heat transfer characteristics, which are given along the concave surface at bigger radial locations and along the extremity end of the turbine airfoil. Film coolant is supplied by two sources which are installed at upstream and downstream positions within the airfoil, such that the ratio of mass flux for the downstream coolant supply BR_d is varied, as the ratio of mass flux for the upstream coolant supply BR_u is approximately constant. Provided for tip gap TG values of 1.20 mm and 2.00 mm are local and line-averaged variations of coefficient of convection ratio, adiabatic film cooling effectiveness, and net heat flux reduction data for specific locations within the recess region, trailing edge region, and upper concave surface region of the airfoil. Associated variations of these surface heat transfer characteristics are related to local levels of turbulent mixing and turbulent shear stress, and to coolant concentrations along and near to the airfoil extremity end surfaces. Resulting coefficient of coefficient ratios, film effectiveness, and net heat flux reduction are often higher for TG = 1.20 mm, relative to the TG = 2.00 mm environment, when compared at the same ratio of mass flux for the downstream coolant supply BRd, and the same airfoil extremity end location.